Centrifugal fluid pump



K. D. M MAHAN CENTRIFUGAL FLUID PUMP March 29, 1966 5 Sheets-Sheet lINVENTOR.

KENTON D. MC MAHAN Filed Dec. 20, 1963 ATTORNEY March 29, 1966 K. D. MMAHAN CENTRIFUGAL FLUID PUMP 5 Sheets-Sheet 2 Filed Dec. 20, 1965INVENTOR.

KENTON D. MC MAHAN ATTORN EY FIG-4.

March 29, 1966 MCMAHAN 3,243,102

GENTRIFUGAL FLUID PUMP Filed Dec. 20, 1963 5 Sheets-Sheet 5 INVENTOR.

KENTON D. MC MAHAN BY W ATTORNEY 5 Sheets-Sheet 4 Filed Dec. 20, 1963INVENTOR. KENTON 0. MC MAHAN FIG.50.

ATTORNEY K. D. M MAHAN CENTRIFUGAL FLUID PUMP March 29, 1966 5Sheets-Sheei 5 Filed Dec. 20, 1963 INVENTOR.

KENTON D. MC MAHAN ATTORNEY United States Patent 3,243,102 CENTRIFUGALFLUID PUMP Kenton D. McMahan, Scotia, N.Y. (Rte. 3, Siry Mountain,Rogers, Ark. 72756) Filed Dec. 20, 1963, Ser. No. 332,987 16 Claims.(-Cl. 230117) The present invention relates to centrifugal fluid pumpsand although particularly adapted to centrifugal blowers or fluid moversof the mixed-flow type having an axial discharge as opposed to the typehaving the usual tangent-ial discharge, some of the features of theinvention can be advantageously employed in connection with other typesof centrifugal fluid pumps. The present invention is such, that some ofthe basic concepts used in the reduction of interstage losses inmulti-stage centrifugal machines by the use of a plurality of radialjets of balanced momentum and disclosed in US. Patent No. 2,868,440 andcopending applications Serial Nos. 175,940 and now Patent No. 3,171,353and 258,033 now Patent No. 3,188,968 can be advantageously employed inconnection with said invention.

In Patent 2,868,440, it was disclosed that if two jets of equalmagnitude (jet velocity X mass) created from the discharge of animpeller of an earlier stage unit are directed in opposed directionsradially inwardly towards the suction eye in alignment along a radialcenter plane and in centered position over the axis of the eye,substantially balanced impact of the two jets is effected as they meetin the vicinity of said suction eye and substantially smooth axialdeflection of said jets into said suction eye is effected as they mergeinto a single stream. By creating diametrically opposed jets of equalmagnitude from each impeller discharge, the rotational velocitycomponents, turbulences, undesired accelerations, eddies and vacuou-spockets in the stream flow between the discharge of a volute of onestage and the intake or eye of a succeeding stage, resulting in socalled interstage losses, and consequent lowering of overall performanceand efficiency of multi-stage machines, are materially reduced.

In cop-ending application Serial No. 175,940, it has been disclosed thatthe radial jets from the discharge of the volutes need not bediametrically opposed to suppress the rotational components and otherundesirable eifects in the said jets, but that these factors disturbingthe efficiency of centrifugal machines can be materially reduced if themagnitude of the radial jets and the spacing therebetween is such thatthe resultant of the radial momentum (jet velocity mass) on one side ofany selected radial plane passing through the axis of the inlet suctioneye is substantially equal to and in substantial radial alignment withthe resultant of the radial jet momentum on the other side of the plane.In accordance with this disclosed concept, an odd number of radial jetpassages properly spaced Will provide the desired jet balance to reduceinterstage losses. It was further disclosed that the tendency of thejets from the perimetric volutes of one stage when turned radiallyinward by a conventional elbow to crowd toward the outer bend and awayfrom the inner bend of said elbow, can be compensated for by the use ofoverbends or overextended bends, whereby a single radial jet of verynearly uniform velocity, mass and direction thereacross and with theresultant of it momentum almost coextensive in position with the radialmechanical centerline of the jet, is produced without the use of innervanes and the like. Also, by this means, the circumferential spacedconfining walls on the circumferential spaced boundaries of the radialjet passages are eliminated. As a result, the radial jets of one stageenter the eye of the next stage with little or no rotational componentsand without measurable loss.

In the copending application Serial No. 258,033, it has been disclosedthat the two overbend elbows may be employed in series for each volutepassage, the function of the first being to arrest the tangentialcomponent of velocity and direct the resultant jet in an axial path, andthe function of the second being to turn the said jet radially inwardwith balanced momentum toward the inlet suction eye of a successivestage impeller or a common concentric discharge passage with uniformaxial velocity.

The present invention contemplates the application of some of the basicconcepts of the aforesaid patent and copending applications to thedesign of a com-pact axial blower having the high flow and pressure headcharacteristics of conventional centrifugal blowers without thenecessity of using the comparatively large and awkward volute collectorscrolls with tangential discharges, and further contemplates thepossible instfllation of such blower units in'series to thereby createmulti-stage blowers in the manner disclosed in the aforesaid copendingapplication Serial No. 175,940, which is not now feasible withconventional blowers.

Another object of the present invention is to provide a new and improvedcentrifugal fluid pump, which is compact, which has a high flow capacityand high efficiency, and which is so designed as to be capable of beingmolded of plastics or made of any other suitable material with a minimumof tooling and unit piece cost.

A further object of the present invention is to provide a new andimproved centrifugal fluid pump, which is designed to reduce overallnoise level particularly by the elimination of or material reduction inblade frequency, or harmonics thereof, or noise components, such asthose normally present in centrifugal blowers operating withconventional scrolls.

To carry out the last object, the discharge from the impeller is dividedinto a plurality of volutes serving as diffusing passages and especiallyshaped to reduce the magnitude of the fluid shock at each volute inletcut-off. To further reduce the noise level of the pump, the number ofsuch cut-offs are chosen so that the ratio of the number of impellerblades to the number of cut-offs is not a whole number. Also, each suchcut-off is axially askewed with respect to the impeller blades by anangle greater than that of the blade spacing of said impeller.

Still another object of the present invention is to provide a new andimproved centrifugal fluid pump designed to attain compactnessnotwithstanding its high flow capacity. To attain this objective, thediffuser or volute passages extend not only radially andcircumferentially but also axially to materially reduce the normallylarge ratio of external diameter to impeller diameter of centrifugalmachines and to substantially eliminate or materially reduce the radialoverlap of such passages and substitute therefor a large axial overlapalong the axial casing of the driving motor. To attain this large axialoverlap andsmall or null radial overlap, the radial diffuser of theaforesaid copending applications has been reduced in radial extent to amean diameter only slightly larger than that of the impeller, and eachvolute passage has been axially shifted abruptly but uniquely around thenext succeeding volute, and has been continued in diverging helical formof extended length around the driving motor. Each volute passageterminates in an elbow which is desirably overextended and which directsthe fluid radially inwardly as circumferentially wall free, jets ofbalanced momentum, in accordance with the teachings of said copendingapplications. The radial jets can be diverted and merged for axialdischarge or for injection into the axial impeller of a succeedingpumping stage.

A still further object of the present invention is to provide a new andimproved generally circular fan or blower unit designed for simplemounting in the wall panel of to electronic or other devices to replacevane-axial, tubeaxial or multi-stage axial fans or blowers.

It is well known that presently existing designs of highly eflicientcentrifugal fluid pumps of the multi-stage type have a comparativelylarge outer diameter as compared to their impeller diameter and henceare unsuitable for many applications. To simply employ one stage fromsuch machines and use it as a blower or fan would be beyond reasonabledesign consideration for a great number of applications because of size,weight and cost factors, in spite of their very high efiiciency and lownoise characteristics. It is further well known that certain designs,having a comparatively small ratio of outer diameter to impellerdiameter and making use of mere turning vanes at the periphery outsidethe impeller, have both low fluid flow and efliciency characteristicscoupled with high comparative noise levels, and thus are also notfeasible for such design purposes. Even with the improved designsdisclosed in the aforesaid applications, the outer diameter of thecasings are over twice the diameter of their respective impellers andnotwithstanding the fact that both the flow and pressure factors arehigh for such machines, neither would be a suitable replacement for anaxial fan or blower in the mass market for small inexpensive blowing orcooling devices as hereinafter further described.

To explain the relative nature of the volume flow capacity of variousknown types of centrifugal machines from liquid pumps throughcompressors to blowers and fans, reference is made to a well recognizeddimensionless quantity, Q/ND where Q represents the inlet flow volume incubic feet per minute, N represents the speed in revolutions per minute,and D represents the diameter of the impeller in feet. In simplifiedform, this factor is the cubic feet of fluid handled per revolution of aone foot diameter impeller measured under its inlet conditions. Typicalflow factors for some well known types of machines may be given asfollows:

Water and liquid pumps .02 to .10 Radial blade centrifugal compressors.10 to .20 Radial blade centrifugal blowers .15 to .30 Improvedmixed-flow compressors .25 to .50 Propeller fans .40 to 1.1 Vane axialfans .50 to 1.1 Mixed-flow blowers with tangential scroll housings .60to 1.5 Squirrel cage blowers with tangential scroll housings .50 to 2.0

The foregoing tabulation of the dimensionless flow factor, Q/ND forvarious typical fluid moving devices serves to better bring into focusthe stated objectives of the present invention and to point up themagnitude of the improvements required to attain such objectives. Itfurther permits a more detailed explanation of the first namedobjective. The term mixed-flow is a generic term applied to fluidimpellers having axially directed blading at their inlet eyes, sometimesreferred to as axial inducers, followed by significant centrifugalblading whereby the fluid particles are acted upon both axially andradially in varying degrees depending upon the flow factor and pressurerequirements. The impellers disclosed in the copending applicationSerial No. 175,940 fell within the meaning of the term and arerepresented in the foregoing tabulations as improved mixed-flowcompressors having a flow factor in the range of .25 to .50. On theother hand, mixed-flow blowers of the present invention are intended forflow factors in the range of .60 to 1.5 to match the flow withtangential scrolls and hence have a relatively larger inlet eye and agreater percentage of axial blading.

Various other objects, features, and advantages of the present inventionwill be apparent from the following description and from theaccompanying drawings, in which:

FIG. 1 is a cut-away side elevation of a centrifugal pump, shown in theform of a blower embodying the present invention;

FIG. 2 is a fragmented transverse discharge end view of the blower shownin FIG. 1;

FIG. 3 is a transverse section of the blower of FIG. 1 taken along thelines 3-3 of FIG. 1 and FIG. 4 and shows a half-section of the axialportion of the volute passages and a half-section at the impeller backplate and the radial portion of the volute passages at the dischargeside of the impeller;

FIG. 4 is a circumferential section taken along the lines 4-4 of FIG. 3and FIG. 5 and shows the axial contour of the volute passages;

FIG. 5 is a transverse section of the blower of FIG. 1 taken along thelines 5-5 of FIG. 1 and FIG. 4 and shown fragmented to show one completevolute passage and its discharge opening;

FIG. 5a is a fragmentary transverse section of the blower similar tothat of FIG. 5 but showing the axial overlap attained with the presentinvention;

FIG. 6 is an enlarged fragmented portion of FIG. 3 to show the askew oroblique angle of one cut-off and the angular spacing of the impellerblades;

FIG. 7 is an enlarged sectional view of one cut-off similar to that ofFIG. 4 but showing the radial overlap of the volute passages;

FIG. 8 is a fragmented side elevation view of the blower of FIG. 1modified to permit it to be mounted in panel walls and the like;

FIG. 9 is a fragmented and cut-away side elevation of a modified blowerdesigned to attain maximum flow rates,

' and FIG. 10 is a fragmented transverse view of one cut-off of theblower of FIG. 9 viewed in the same direction as that of FIG. 6 of theblower of FIG. 1.

Referring to FIGS. l6 of the drawings, there is shown a centrifugalfluid pump 10 and more specifically a single stage centrifugal blowerunit for handling air or gases at comparatively low pressure heads andintended for installation in a simple duct or pipe of uniform size andcrosssection, although as far as certain aspects and features of theinvention are concerned, the blower with minor variations may have anynumber of stages mounted concentrically on a single shaft or any numberof complete singlestage blowers may be used in series to form amulti-stage assembly.

The blower unit 10 comprises a skeleton type motor 11 mounted axially ofthe unit in suitable elastic mountings 12 and having a shaft 13 on whichis mounted an impeller 14 secured to shaft 13 by a set screw 15. Theblower 10 also comprises a circular impeller casing 16, an axialdiffuser casing 17 and a discharge casing 13, these casings beingsecured end to end. The axial diffuser casing 17 contains as its innerperiphery a cylindrical motor compartment housing 20, with an inner endmotor support 21 for receiving one of the elastic mountings 12.Similarly, an opposite end motor support 22 is adapted to receive theother elastic mounting 12. The mountings 12 are restricted againstrotation in the supports 21 and 22 by suitable lugs 23 respectively, andare cemented or otherwise rigidly attached to motor bearing shields 25.The support 22 is secured to the end wall of the casing 17 by screwstuds 26 and the discharge casing 18 is likewise secured to the casing17 by means of screw studs 27 threaded into tapped stud spacers 28 andinto bosses 29 on said casing 17.

While the motor 11 is shown mounted in elastic mountings 12, it isunderstood that such mountings may not be needed where the entire blowercasing 16, 17 and 18 is molded with any one of several comparativelyflexible plastic materials as contemplated. In such cases, the

motor may be rigidly secured to support 22 or otherwise mounted.

The support 22 contains a circumferential row of holes 30 to permit freecirculation of air or gas around the motor windings 31 for cooling.Motor leads 32 pass through a suitable grommet 33 in the support 22 ad asimilar grommet 34 in the wall of casing 17. The discharge casing 18contains on its inner periphery a discharge flange 35 upon which asuitable discharge duct or a hose and clamp (not shown) may be attached.Similarly, the impeller casing 16 contains on its inner periphery aninlet flange 36 on which is pressed or shrunk an inlet orifice 37 havingthe same outer flange diameter as the opposite end flange 35 for thesame or similar connection.

The impeller 14 comprises a backplate 40, an inlet shroud 41 and aplurality of circumferentially spaced blades 42 mounted therebetween andso shaped that they are concave on their leading faces and generallyforwardly curved at their outer peripheries or discharge ends 43 asrespects their direction of rotation. The impeller blades 42 have inletportions 44 inclined outwardly and forwardly to form an axial inducersection and to efiiciently receive the flow from the eye of inletorifice 37 in a shock free manner. The blades 42 so designed also serveto increase greatly the flow factor of such mixedflow impellers. Theimpeller blades 42 receive the flow from the inlet orifice 37 in asubstantially axial direction at their inlet portions, impel it first ina generally axial direction and then change it gradually, by thecentrifugal action and the shape of the blades, to a generally radialdirection until it is discharged at the discharge end 43 of the bladesin said radial direction. Depending upon the desire-d flow-pressure headcharacteristics, the discharge ends 43 of the blades 42 need not havethe same diameter at the backplate 40 as at shroud 41 and the flowdischarge from said blades need not be in a radial direction as regardsthe axis of the impeller but may contain an axial component as well as aradial component.

Around the impeller 14 is a radial receiver passage 45 of minimum radialextent and comprising an inlet wall 46 and a backplate wall 47 mountedon a rabbeted surface 48 of the motor support 21. Around the receiverpassage 45 are a plurality of cut-offs 50, five being shown equallyspaced and of equal dimensions, forming the inlets to combined radialvolute and axial diffuser passages 51 formed by vane assemblies 52within the impeller cas ing 16 and axial casing 17. Each vane unit 52comprises .a proportionate section of the backplate wall 47, a.corresponding-cut-oif 50, a radial volute section 53 within the impellercasing 16, an axial diffuser section 54 between the outer and innercircumferential walls of axial diffuser casing 17 and a wedge-shapedfiller 55 to serve the dual purpose of gradually reducing the innerdiameter of the volute passage from that of the backplate wall 47 downto that of the motor compartment housing 20 and to facilitate thedivergence of the passage inwardly and thus effectively reduce therequired outer diameter of the casing. Each of said vane units 5-2 issecured to the casing 17 by a screw stud 56 passing through the end wallof said casing and by two screw studs 57 threaded into the motor support21, and is also secured to the impeller casing 16 by a screw stud 58passing through the end wall of the casing 16. The vane assemblies 52thereby serve not only as flow passages but also as a means of securingcasing 17 to casing 16 with the assistance of a rabbeted joint 59between casings 16 and 17. While the vane assemblies 52 are shown madeup of separate units, they could just as well be formed as a singlemulti-vaned assembly and inserted within the blower casing in the sameor similar manner. Additionally, each said vane assembly 52 contains adead space between the outer walls of radial volute section 53 and theinner" circumferential and end walls of casing 16 (shown seetionally inFIG. 8), which simplifies the design and construction of casing 16 andthe molding of the vane assemblies but could be eliminated byappropriate shaping of the end wall of casing 16.

The aforesaid dead space serves as an area adjusting means forcontrolling the rate of divergence of the radial volute section 53 inconformity with the design characteristics of impeller 14, and furtherserves to distinguish the present invention from prior art machines suchas represented by U.S. Patent No. 3,069,071 which shows acircumferential receiver, outside the impeller discharge, devoid of anyform of radial volute passages.

Located at the inner ends of volute passages 51 around the impeller 14are the cut-offs 50 radially spaced by a minimum clearance from thedischarge ends 43 of the impeller blades 42. In the preferred form ofthe invention shown, this clearance is approximately 3% of the impellerdiameter but as far as certain aspects of the invention are concerned,may vary from the least allowable operating clearance to that of avaneless diifu-ser between walls 45 and 47, such as described in thecopending applications. The inlet edges of the cut oifs 50 are axiallyaskewed from the inlet wall 46 to the backplate wall 47, i.e. the inletedges of the cut-offs 50 extend obliquely with respect to a plane atright angles to the impeller axis. These cut-oifs 50 are axially askewedby a circumferential cut-ofi spanning angle (FIG. 6)

' defined as the angle between a radial plane, passing through theimpeller axis and through the tip of the cutofi 50 at its junction'withinlet Wall 46 and a similar radial plane passing through the other tipof the cut-off at the point of junction of the cut-off with its sectionof backplate wall 47. This angle p is greater than the radially outerimpeller spacing angle 0 measured similarly be tween the radial planesof successive impeller blades; In the specific form shown, the angle isapproximately 26 while the angle 0 between sucessive blades isapproximately. The ratio between the angle 3 and the angle 0 must be atleast one but desirably less than 2.0, except that angle :1: should beat least 20.

it is well known that the cut-off of centrifugal blowerhousings is amajor source of noise of such devices and various means have beenemployed to reduce or absorb such noise at its source. Reference is madeto U.S. Patents 2,107,897, 2,160,666, 2,171,341 and 2,171,342. Thesevarious methods and others have hadvaried success in reducing in blowersthe blade frequency and their harmonics to acceptable levels. However,any and all these known methods require a comparatively large clearancebetween such cut-off and the impeller blades ranging from a minimum of5% of the impeller diameter to upwards of 8% or more and further requirethat these cut-offs be comparatively blunt. These factors are a cause ofboth reduced performance and efiiciency over a closely spaced, sharpedged cut-01f. It has been 'found in accordance with the presentinvention that this objectionable type of noise is substantiallyeliminated by askewing said cut-off by a cut-off spanning angle equal toor greater than the radially outer impeller spanning angle 6 necessaryto span the space between successive impeller blades and that with thisinvention, the requirements for clearance, bluntness and all the othermeans employed in the prior art to control noise are eliminated.

This permits a cut-off designed solely for performance and ease ofmanufacture.

Since the ratio between the number of impeller blades (nineteen) and thenumber of cut-offs 50 (five) is not a whole number, this mix numberrelationship further tends to .cut down harmonics and resonances tendingto create noises.

The volute passages 51 starting at the cut-offs 50 continue, in adiverging manner to. convert the high velocity at the impeller dischargeinto static pressure head, at first in a generally radial directionwithin the radial volute section 53. Then the volute passages 51 aregradually directed and shunted axially between the outer circular Wallof casing 17 and the outer surface of wedge-shaped filler 55 and thecircumferential motor compartment housing 20, separated by the axialdiffuser section 54 of the vane assembly 52 and terminate in overbendsor overextended elbows containing an inner bend 61 having a protuberance62 and an overextended outer bend 63. The resultant fluid jets issuesubstantial axially from the elbows 60 and are then directed radiallyinwardly by a second overbend elbow, containing in combination thecurved surface 64 of casing 18 with its concentric protuberance 65forming an overextended outer bend, and a slightly overextendedintermediate vane 66, to direct the jets over the concave surface 67 ofthe motor support 22 and to the common axial discharge orifice 68 withinthe discharge flange 35.

As fluid goes through an elbow, it tends to crowd towards the outer bendof the elbow and away from the inner bend due to centrifugal action, sothat the resultant momentum of the jet, ie the jet velocity times itsmass, is offset from the positional centerline of the jet passage at theoutlet of the elbow. This adverse condition is substantially nullifiedby shaping each elbow 60, so that the momentum of the elements of eachjet emerging from the elbow is substantially uniform across the elbowfrom the inner bend to the outer bend. For that purpose, the inner bend61 on the upstream side of the elbow 60 from which the stream tends tobreak away as it flows through said elbow, turns through an angle onlysulficiently to direct the stream from the corresponding volute passage51 in an axial direction but the outer bend 63 at the downstream side ofthe elbow has an overbend, i.e. turns through an angle greater than thatsufficient to direct the stream in an axial direction. The effect ofthis overbend in the elbow 69 is to compensate for the tendency of thestream to crowd towards the outer bend 63 and to cause thereby theresultant momentum'of the jet entering the passage at the outlet of theelbow to be almost coincident with the centerline of the passage. Thefunction of the overbend elbow 60 is described in detail in theaforesaid copending applications.

Another aid in preventing the stream passing through the elbow 60 frombreaking away from the inner bend 61 of the elbow is the protuberance 62on said bend to deflect the approach stream away from the immediate areaof the bend to crowd said stream around and over said protuberance intothe sides of the passage at the outlet of the elbow and thereby increasethe actual and effective radius of the inner bend. The function of thisprotuberance 62 is also described in detail in the aforesaidapplication.

The overex-tension of the outer bend in the casing 18 with itsconcentric protuberance and its slightly overextended intermediate vane66 serves a function similar to that described with reference to theelbow 60 with its overextended outer bend 63 and its protuberance 62 onits inner bend.

As a result of the construction described, the five equally spacedbalanced streams of equal magnitude free from confiningcircumferentially spaced stream separating walls course radialy inwardlyin the casing 18 and merge as they meet near the inlet of the axialdischarge orifice 68. As a result of the construction described, therotational velocity components, turbulences, undesired accelerations,eddies and vacuous pockets in the stream are reduced materially beforeand as they enter the axial discharge orifice 68, so that the merging ofthe streams in this orifice is accomplished smoothly with minimum lossof efiiciency.

The functions of the overbend elbows and the Wall means for theproduction of radial jets of balanced inward momentum and theircombination into a single axial dis charge stream are similar to thosedescribed in detail in the aforesaid copending applications, except thatthe second overbend in this invention contains the intermediate vane 66of lesser overbend proportions to further contribute to the efiicientturning of the jets from axial to radially inward. The need for such avane or vanes arises because of the high aspect ratio (ratio of thedepth of the stream perpendicular to the axis of the bend to that of itswidth parallel to said axis) of the bend and the desirability ofminimizing the axial space required to accomplish the reduction indischarge diameter. As far as certain applications and uses areconcerned, the intermediate vane 66 may be omitted, and further it iswithin the broad scope of the invention to dispense entirely with thesecond overbend elbow and make use of a single overbend elbow at theterminus of each passage to direct the jets radially inward or at anyangle from an axial direction to radial inward direction with balancedmomentum in accordance with the teachings of copending applicationSerial No. 175,940 to thereby obtain any desired discharge convergence.

Cne of the important objectives of the present invention is to reducethe normally large outer diameter of centrifugal blowers, while at thesame time permitting a greater than two fold increase in the flow factornormal for such machines. This is accomplished in the present inventionby the substitution of combined radial-axial volute and diffusingpassages for the usual overlapping radial volute passages together withthe use of the axial space over the driving motor which would otherwisebe wasted. This is possible in the present invention as an added resultof and in combination with the askewed cut-off 50 previously describedin detail. This askewed cut-off 5% permits a gradual and orderlyconversion of the normal radial volute to an axial passage withsubstantially little or no radial overlap of successive volutes. Forpurposes of describing this feature of the invention and to distinguishfrom prior art machines, consider a radial plane rotatable about theaxis of the impeller and having an axial width equal to the spacingbetween the inlet wall 46 and backplate wall 47, or the equivalent,radial overlap may be considered to occur when any radial element of, orradial line on, the said plane intercepts any wall separating anyportion of one jet from the adjacent jet. The term radial overlap asherein used is expressed as the percentage of the total projections ofsaid intercepted areas on the total cylindrical surface having the meandiameter and axial width of the fluid receiver 45, or its equivalent.Similarly, axial overlap may be considered to occur when any axialelement of a radial plane rotatable about the impeller axis, or any lineon said plane parallel to the axis, intercepts any wall separating anyportion of one jet from an adjacent jet having common directionalcomponents. The term axial overlap as herein used is expressed as thepercentage of the total of the projections of the said intercepted areason the total circumferential area between the impeller backplatediameter and the outer contour of the housing inner wall.

Referring to FIG. 7, the projection of the total intercepted area ofeach volute passage by radial elements of a radial plane passing throughthe axis of the impeller is bounded by the construction lines aroundarea X, and for the purpose of the present invention shown, the radialoverlap need not exceed 15 to 25% to effect an orderly axial shift ofone volute passage around the next succeeding passage and could withslightly reduced performance be entirely eliminated. In the specificform shown, the radial overlap is approximately 17%. This radial overlapis exceedingly low as compared to the usual to 200% radial overlap foundin conventional multi-volute centrifugal pumps. The radial overlap ofthe invention shown in copending application Serial No. 175,940 isapproximately 100%.

Referring to FIG. 5a, the projection of the intercepted area of apreceding passage with respect to a chosen passage by axial elements ofor lines on a radial plane passing through the impeller axis isrepresented within the construction lines around area Y and theadditional intercepted area of the succeeding passage is representedwithin the construction lines around the smaller area Y the total axialoverlap is represented by an area equal to area Y plus area Y This axialoverlap is desirably above 75 In the specific embodiment of theinvention shown, the axial overlap is approximately 78%, compared tosubstantially in the machines of the aforesaid copending applications.

The combined radial and axial overlaps must exceed 75% and desirablyshould total approximately 100% or higher for maximum conversion of thehigh velocity head at the impeller discharge into static head forelficient overall performance. In the preferred form of the presentinvention, the ratio of axial overlap to that of the radial overlap mustbe greater than 2.0 and desirably should be as high as 4.5 or higher.

Thus, there has been created in accordance with the present invention, adiffuser for converting velocity head to static head that is the exactconverse of the mixedflow impeller in that it receives the stream athigh radial velocity from the impeller discharge and gradually changesits direction into an axial one while at the same time reducing itsvelocity.

Referring to FIG. 8, the blower of FIG. 1 with discharge casing 18removed is shown mounted in a metal panel 70, such as might representthe outer wall of a cubical enclosure, by five symmetrically spacedservo mounts 71, each comprising a screw 72, a nut 73, a lock-washer 74and a heavy washer 75 having a milled out crescent recessv 76 forming acrescent shaped tongue extending into a correspondingly milled recess 77formed-in the casing 16 (FIG. Similar recesses 77a are likewise milledin casing 17 to permit a similar mounting in a panel 70 at the oppositeend, to permit a reversal of the flow direction by turning the completeblower unit around or other mounting considerations, To furtherfacilitate the mounting of the blower unit in the panel 70, circularrabbeted flange 78 is provided at the endtof casing 16 to fitconveniently into a round hole in the panel 70, and a like rabbetedflange 78a is also provided on casing 17 for like panel mounting but isused additionally for the mounting of casing 18 to casing 17. comes anaxial blower having centrifugal performance and 'efliciency and suitableas replacements for vane-axial or similar devices of lower efiiciencyand much higher noise levels. Although the milled recesses 77 and 77aare shown as symmetrically spaced, it is understood that any spacing ornumber could be used, or continuous circumferential grooves might besubstitutedtherefor without departing from the broad concepts of thepresent invention.

Referring to FIGS. 9 and 10, there is shown a modified form of thepresent invention affording the highest possible flow factor with thesame outside diameter and employing an impeller of larger inlet diameterand blading of larger diameter at the inlet shroud than at thebackplate. In the modified form, impeller 14a is driven by motor 11athrough shaft 13a in the same manner as described for the blower of FIG.1 and comprises a backplate 40a, an inlet shroud 41a and a plurality ofblades 42a therebetween. The outer diameter of the inlet shroud 41a andthe outer discharge ends 43a of the blades 42a at the said shroud islarger than that of the backplate 40a thus providing a conical shapeddischarge which permits the largest possible radial space between theimpeller backplate 40a and the other wall of casings 16a and 17a tohandle the higher flow from said impeller in an efficient manner. Aroundthe outside of the impeller 14a is located a plurality of cut-offs 50a,five being used, askewed by the cut- The blower so mounted be offspanning angle a of higher value than the radially.

outer impeller spacing angle 0a between successive blades 42a, andfurther radially askewed between passage walls 46a and 47a by an amountequal to the difference between r and r sufiicient'to maintain aconstant radial clearance between said cut-offs and the discharge ends43a of the blades 42a. The cut-offs 5011 form the entrance toradialaxial volute passages 51a separated by vane assemblies 52awhich'terminate in overbend elbows 60a in the same man: ner aspreviously described.

Further in the modified form of the present invention shown in FIG. 9,the cylindrical motor compartment housing 20 of the blower of FIG. 1 hasbeen eliminated for the combined purposes of (1) conserving radial spaceover the motor, (2) providing a maximum of ventilation for the saidmotor, and (3) eliminating the additional weight and cost of the saidhousing. Thecentrifugal forces on the fluid particles due to theircircumferential motion in the radial volute and axial diffusing passages51a tend to keep the streams confined to their respective passages without the need for the inner confining wall. Hence, the inner peripheryofthe axial diffusing passages may be wall-free in the manner of thepreviously described circumferential wall-free stream passages withindischarge casing 18, or the outer diameter of the driving motor 11a maypartially serve as such a confining wall.

7 While the modified blower of FIG. 9 operates efliciently at theextremely high flow factors for mixed-flows blow-t ers within a minimumoutside diameter of easing, it has limited suitability and efliciencyfor multi-stage operation because some of the requirements forsuppressing eddies, turbulences and vacuous pockets in the dischargestream have been traversed in this modified specie of the invention Anysimple and inexpensivelmeans for reducing the required number and/orcomplexity of sizes is of extreme economic importance. It is believedthat the present invention fulfills that desideratum.

The improved blower of the present invention affords simple andinexpensive means for varying the performance over a wide range Withinthe same housing and the same basic impeller by reducing its outerdiameter in convenient'steps, usually by reducing the diameter of thebackplate 40 by a greater percentage than that of inlet 41,

and still maintain its inherent high efiiciency. As the outer diameterof the impeller is reduced, the inlet wall 46 and the backplate wall 47form a vaneless difiuserfor partially converting the high velocity atthe impeller discharge into static head in an efiicient manner prior toreaching the cut-offs 50. It is to be. understood that the broadconcepts of the invention permit such latitude in impeller design withinthe same housing or the cut-offsSt] may be extended into said diffuserto form a vaned diffuser askewed in the manner described to obtain anydesired I performance characteristics. Further, while the improved axialhousing is shown for a mixed-flow type impeller and it is particularlywell suited to this type due to its high flow factor, other impellerdesigns having a relatively low ratio of discharge width to impellerdiameter, of the order of .25 or less, would operate satisfactorily.

In'the following claims, radial overlap and axial overlap are intendedto mean the overlaps hereinbefore described.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto but is to be construed broadly and restricted solely bythe scope of the appended presenting an inlet cut-off edge near thedischarge periphcry of said impeller extending obliquely with respect toa plane at right angles to the impeller axis.

r l l centrifugal fluid pump as described in claim 1, wherein the volutepassages have radial, circumferential and axial flow components, thecircumferential flow components being in the direction of rotation ofthe impeller, each of said cut-off edges extending obliquely from theinlet side of the pump in a direction having a circumferential componentin the direction of rotation of the impeller.

3. A centrifugal fluid pump comprising an impeller having a plurality ofequally spaced blades, and means forming a plurality of volute passagesextending around the discharge periphery of said impeller and eachpresenting an inlet cut-off edge near the discharge periphery of saidimpeller extending obliquely with respect to a plane at right angles tothe impeller axis, the ratio between the number of blades in saidimpeller and the number of cutoff edges being other than a whole number.

, 4. A centrifugal fluid pump having an inlet and an outlet andcomprising an impeller having atplurality of spaced blades, and meansforming a plurality of volute passages extending around the dischargeperiphery of said impeller and each presenting an inlet cut-off edgenear the discharge periphery of said impeller extending obliquely withrespect to a plane at right angles to the impeller axis, the radius ofthe blades to the outer tips thereof on the sides of the blades nearestthe inlet ofthe pump being substantially the same as the radius of theblades to the outer tip thereof on the side of the blades furthest fromthe inlet of the pump, whereby the outer discharge edges of the bladesconjointly define a cylindrical outline.

, 5. A centrifugal fluid pump having an inlet and an outlet andcomprising an impeller having a plurality of spaced blades, and meansforming a plurality of volute passages extending around the dischargeperiphery of said impeller and each presenting an inlet cut-01f edgenear the discharge periphery of said impeller extending obliquely withrespect to a plane at right angles to the impeller axis, the radius ofthe blades to the outer tips thereof on the sides of the blades nearestthe inlet of the pump being greater than the radius of the blades to theouter tips thereof on the side of the blades furthest from the inlet ofthe pump, whereby the outer discharge edges of the blades conjointlydefine a substantially conical outline.

6. A centrifugal fluid pump comprising animpeller having a plurality ofequally spaced blades, means forming a radial receiving passage aroundsaid impeller and comprising an inlet wall and a back Wall, meansforming a plurality of volute passages extending around the dischargeperiphery of said impeller and each presenting an inlet cut-off edge insaid receiving passage located between said walls near the dischargeperiphery of said impeller and extending at an oblique, angle withrespect to a plane at right angles to the impeller axis, each of saidcut-oif edges terminating at its tips near said walls respectively, thecut-off spanning angle between two radial planespass: ing through theimpeller axis andthe tips respectively of said cut-off edge beinggreater than the radially outer impeller blade spacing angle between tworadial planes pass ing through the corresponding radially outer edgesections respectively of successive impeller blades. 7

7. A centrifugal fluid pump comprising an impeller having a plurality ofequally spaced blades, means forming a radial receiving passage aroundsaid impeller and comprising an inlet Wall and a back wall, meansforming a plurality of volute passages extending around the dischargeperiphery of said impeller and each having radial, circumferential andaxial flow components, the circumferential flow components being in thedirection of rotation of the impeller, each of said volutes presentingan inlet cut-01f edge in said receiving passage located between saidwalls near the discharge periphery of said impeller and extending at anoblique angle with respect to a plane at right angles to the impelleraxis from said inlet wall in a direction having a circumferentialcomponent in the direction of rotation ,of the impeller, each of saidcut-off edges terminating at its tips near said walls 12 respectively,the cut-off spanning angle between two radial planes passing through theimpeller axis and the tip respectively of said. cut-off edge beinggreater than the radially outer impeller blade spacing angle between tworadial planes passing through the corresponding radially outer edgesections respectively of successive impeller blades, the ratio betweenthe number of blades in said impeller and the number of cut-0ff edgesbeing other than a whole number.

8. A centrifugal fluid pump. comprising an impeller .With an axialinlet, a motor coaxial with said impeller for driving said impeller,,anaxial discharge, means forming a plurality of volute passages extendingaround the discharge periphery of said impeller and each presenting aninlet cut-off edge near the discharge periphery of said impeller, eachof said volute passages having radial, circumferential and axial flowcomponents, said passages extending helically around said motor andterminating in respective elbows turned to direct the fluid radiallyinwardly towards said axial discharge, said passages extending withstreamline continuity from the discharge periphery of said impeller tosaid elbows respectively.

9. A centrifugal fluid pump comprising an impeller of the mixed flowtype, and means forming a plurality of volute passages extending aroundthe discharge periphery of said impeller and having streamlinecontinuity along their full lengths, said passages having radial andcircum- :ferential flow components as well as axial flow components,said pump having an axial overlap substantially greater than the radialoverlap.

It A centrifugal fluid pump comprising an axial impeller of the mixedflow type, a casing surrounding said impeller and extending axially asubstantial distance beyond said impeller, said pump having an axialinlet for said impeller near one end of said casing and an outlet nearthe other end of the casing, and means forming a plurality of diffusingvolute passages extending with streamline continuity from regions nearthe discharge periphery of said impeller radially, circumferentially andaxially along said casing to said outlet, said ump having an axialoverlap substantially greater than the radial over-lap.

r 11. A centrifugal fluid pump as described in claim 10, wherein saidoutlet .is anaxial one, and said casing has means for directing thestreams from the discharge ends of said volute passages radiallyinwardly towards said axial outlet. 1

12. A centrifugal fluid pump having an inlet and an outlet andcomprising an axial impeller, and means form- .ing a plurality ofditfusing volute passages around the discharge periphery of saidimpeller, said volute passages extending from the discharge side of saidimpeller to said outlet with streamline continuity radially,circumferentially and axially and having less than 25% radial overlapand more than 75% axial overlap.

. 13. A centrifugal fluid pump as described in claim 12, wherein saidpump includes a casing with said inlets and outlets coaxial andextending at opposite ends of said casing.

14. A centrifugal fluid pump comprising a peripheral casing, an inletand an outlet near opposite ends of said casing, an impeller on thedischarge side of said inlet located between said inlet and said outlet,a motor in said casing for driving said impeller located between saidimpeller and 'said outlet and having its outer periphery spaced radiallyinwardly from said casing, means forming a plurality of volute passagesextending around the discharge periphery and around the motor towardssaid outlet withstreamline continuity and having radial, circumferentialand axial flow components, with said volute passages having an axialoverlap substantially greater than the radial overlap.-

15. A centrifugal .fluid pump as described in claim 14,

wherein the inner peripheries of the parts of said volute passagesextending around said motor are provided with W W p pher l Walls aroundsaid motor separating the :chamber enclosing said motor from said volutepas- 2,139,112 12/1938 Catranis 230130 sages. 2,331,299 10/1943 Blorn103109 16. A centrifugal gas pump as described in claim 14, 2,474,6116/1949 Wylie 230-42 wherein the inner peripheries of the parts of saidvolute 2,476,692 7/1949 Bernstein 230-42 passages extending around saidmotor are wall-free, 5 2,868,440 1/1959 McMahan 238130 whereby the innerperipheries of the parts of the volute passages extending around saidmotor are in free eorn- FOREIGN PATENTS munication with the chamberenclosing said motor. 75 347 12/1954 h 1 3 222 2 ifi g ifggfig 10 ROBERTM. WALKER, Primary Examiner.

DONLEY J. STOCKING, MARK NEWMAN,

1,275,672 8/1918 Goss 230127X 2,002,907 5/1935 Sessions 103 s7 V

8. A CENTRIFUGAL FLUID PUMP COMPRISING AN IMPELLER WITH AN AXIAL INLET,A MOTOR COAXIAL WITH SAID IMPELLER FOR DRIVING SAID IMPELLER, AN AXIALDISCHARGE, MEANS FORMING A PLURALITY OF VOLUTE PASSAGES EXTENDING AROUNDTHE DISCHARGE PERIPHERY OF SAID IMPELLER AND EACH PRESENTING AN INLETCUT-OFF EDGE NEAR THE DISCHARGE PERIPHERY OF SAID IMPELLER, EACH OFVOLUTE PASSAGES HAVING RADIAL, CIRCUMFERENTIAL AND AXIAL FLOWCOMPONENTS, SAID PASSAGES EXTENDING HELICALLY AROUND SAID MOTOR ANDTERMINATING IN RESPECTIVE ELBOWS TURNED TO DIRECT THE FLUID RADIALLYINWARDLY TOWARDS SAID AXIAL DISCHARGE, SAID PASSAGES EXTENDING WITHSTREAMLINE CONTINUITY FROM THE DISCHARGE PERIPHERY OF SAID IMPELLER TOSAID ELBOWS RESPECTIVELY.